INHIBITION BY BACITRACIN OF SOME HYDROLYTIC ENZYMES

Abstract

Bacitracin was seen to inhibit noncompetitively the papain‐catalyzed hydrolysis of N‐benzoyl‐DL‐arginyl‐2‐naphthylamine and the hydrolysis of N‐L‐leucyl‐2‐naphthyl‐amine catalyzed by subtilisin, papain, and leucine aminopeptidase. Alkaline phosphatase of E. coli, aminopeptidase B of rat liver, and trypsin were not affected to any noticeable extent. α‐Chymotrypsin was only slightly inhibited. The bacitracin preparation studied was not found to contain zinc (when determined with an atomic absorption spectrophotometer). The values of K i for the inhibition of papain, subtilisin, and leucine aminopeptidase were determined to be 5.0, 4.5, and 2.0 mM, respectively. The values of the maximum velocity, V, and the substrate constant, K s , at different concentrations of bacitracin were calculated for trypsin, papain, subtilisin, and leucine amino‐peptidase by the aid of a computer program using the Hanes' equation. Bacitracin also inhibited some aminopeptidase‐like enzymes of human fetal liver, human oral fluid, and gingiva. The enzymes hydrolyzing N‐L‐leucyl‐2‐naphthylamine were the strongest inhibited and those hydrolyzing N‐L‐prolyl‐2‐naphthylamine the least inhibited. The selective effect of bacitracin was explained in terms of substrate specificity of the enzymes and in terms of different topology of enzyme surface around the active site. The enzymes which were inhibited more strongly (papain, subtilisin, and leucine aminopeptidase) were considered to be inhibited due to the “open” structure of their active centers.